Error when viewing object with null prototype

[msrose]

Reproduction:

let o = Object.create(null)
> undefined
o
> Object {}

Trying to "expand" the object by clicking the arrow is fine here - no properties are shown.

o.a = 'hi'
> "hi"
o
> Object {}

When trying to expand the object now to view its poperties, the following error appears in the console:

TypeError: _this2.props.object.propertyIsEnumerable is not a function

Mancy version is 3.1.0